In an internal combustion engine, there is provided a control device which calculates an appropriate injection amount according to a driving state and controls a fuel injection valve to supply the fuel. A magnetic force generated by a current flowing to a coil built in the fuel injection valve for opening and maintaining an open state of the fuel injection valve is asserted to a valve body of the fuel injection valve, so that the valve body is opened or closed and the fuel is injected by the corresponding amount according to a valve-opening period.
Herein, the amount (the injection amount) of the injected fuel is mainly determined by a differential pressure between a pressure of the fuel and an atmosphere pressure of an injection port of the fuel injection valve and a time period during which the open state of the valve body is maintained and the fuel is injected. However, regarding the injection amount of the fuel injection valve, it is known that a variation is caused in an injection flow rate of each fuel injection valve by a variation in manufacturing processes of the fuel injection valve at an initial stage and a secular degradation of the fuel injection valve after being mounted in the internal combustion engine. Therefore, in a case where the variation in the injection amount of the fuel injection valve is large, an air fuel ratio control of the internal combustion engine is damaged in accuracy, and exhaust emission performance and drivability are affected. Therefore, it is necessary to more accurately control the fuel injection flow rate with respect to the variation of the fuel injection valve in order to inject an appropriate amount of fuel.
In order to solve the problem, it is generally known that the air fuel ration sensor is provided in an exhaust pipe of the internal combustion engine, and a feedback control to the fuel injection or an air fuel learning control is performed to make an exhaust air-fuel ratio be a desired air fuel ratio based on the output of the air fuel ration sensor.
In addition, as a method of handling a change in a valve-opening response and a valve-closing response of the fuel injection valve, PTL 1 discloses the description “there is disclosed a control device which compares a valve-opening delay and a valve-closing delay of the fuel injection valve with an initial valve-opening delay and an initial valve-closing delay to detect a change amount, and corrects a drive pulse based on the detected change amount. According to the control device, it is possible to suppress the degradation with time of the fuel injection valve and a change in the injection amount caused by an abnormality while supplying an appropriate fuel amount at any time”.